1. Field of the Invention
The present invention relates to a method of producing a nozzle plate, more particularly to a nozzle plate having nozzle holes with an extremely small diameter, with high mechanical strength and excellent water and ink repellency, for an ink jet head for use in an ink jet printer.
2. Discussion of Background
As conventional ink jet heads, there are known a bubble jet type ink jet head and a pressure application type ink jet head. In an ink jet head of the bubble jet type, bubbles are formed, using an exothermic heating element such as a thermal head disposed in an ink passage of an ink reservoir, which is connected to the nozzle holes of the ink jet head, so that an appropriate amount of the ink is ejected from the nozzle holes by the pressure applied to the ink by the bubbles, while in an ink jet head of the pressure application type, pressure is externally applied in a pulse-like manner to the ink filled in the ink reservoir, using pressure application means such as a piezo-electric element, so that an appropriate amount of the ink is ejected from the nozzle holes by the pressure applied to the ink by the pressure application means.
For producing the nozzle plates for use in such ink jet heads, many methods have been proposed, for instance, in Japanese Laid-Open Patent Application 6-99581 and Japanese Laid-Open Patent Application 7-314669, which respectively disclose an invention entitled "Method of Producing Nozzle Plate" and an invention entitled "Ink Jet Recording Head and Method of Producing the same".
As working methods for forming the nozzle holes in the above-mentioned nozzle plates, there are known, for instance, an injection molding method using a resin as a injection molding material, a punch press working method using a punch and a die, an etching method and an additive method which are known as methods of producing mainly nozzles made of metallic materials, and an abrasion method for working resins such as polyimide, polycarbonate, polysulfone, polyethersulfone, and polypropylene, by ultraviolet irradiation, for instance, using excimer laser beam.
When the nozzle holes are formed in the nozzle plate, for instance, by the injection molding method or the punch press working method, the edges of the nozzle holes tend to be rounded or to become blunt, or burrs are formed at the edges, or the worked surface is rough, so that the surface of the nozzle plate worked by these methods has poor ink and water repellency and therefore the ink tends to stick to the surface of the nozzle plate or the nozzle holes tend to be clogged with the ink.
Furthermore, there is a lower limit to a minimum diameter of the nozzle holes that can be made by these methods, since there is a limit to both the minimum size of the holes in the metal mold and the minimum diameter of the punch that can be used in the above methods. To be more specific, it is extremely difficult to form nozzle holes with an inner diameter as small as several microns by the above methods.
In the above-mentioned etching method or the additive method, many treatment and processing steps are required, and after the nozzle holes are formed, mirror polishing of the nozzle plate surface, or a secondary treatment such as nickel.teflon composite plating has to be performed in order to improve the water repellency of the surface of the nozzle plate, so that the production cost of the nozzle plate is high.
The abrasion method using the excimer laser has a significant advantage over other methods that shavings or powder-like turnings are not formed in the course of the working process. However, in the case of the abrasion method using the excimer laser, the edge portions of the worked nozzle holes on the ink ejection side tend to be slightly rounded although the extent thereof differs more or less depending upon the intensity and the duration of the irradiation of the nozzle formation surface with the ultraviolet light.
Even in the case of the nozzle holes worked in the nozzle plate by the above-mentioned abrasion method using the excimer laser, the nozzle holes and the nozzle plate have so poor water repellency that the nozzle holes on the ink ejection side tend to be clogged with the ink which sticks to the surface of the nozzle plate, in the same manner as in the case of the nozzle holes worked by the above-mentioned other methods.
Furthermore, as mentioned above, in the case of the abrasion method using the excimer laser, resins such as polyimide, polycarbonate, polysulfone, polyethersulfone, and polypropylene, are used in the form of a relatively thin plate in order to facilitate the abrasion working thereof using the excimer laser, so that the nozzle plate made by the abrasion method using the excimer laser has less mechanical strength than that of a nozzle plate made of a metal.